Methods of welding stacks of thermoplastic material to one another without the use of an ancillary adhesive material are generally known in the art. Heat sealing and ultrasonic bonding have often been used in such prior art processes. Many such prior art bonding processes are static, i.e., there is little or no lateral movement between the pieces being bonded and the bonding apparatus.
Typical of prior art processes which utilize heat to soften two or more polymeric layers and bond them to one another is U.S. Pat. No. 4,519,798 issued to Dinius on May 28, 1985. Dinius discloses a disposable diaper structure wherein an absorbent core is encapsulated between a multiplicity of sheets. Each of the sheets is constructed of a material, such as polyethylene, which will heat seal without the necessity of an adhesive. The diaper is made by heating and sealing the overlapping edges of the polyethylene sheets directly to one another outside the borders of the absorbent core.
Representative of prior art continuous web bonding processes using ultrasonic bonding systems is U.S. Pat. No. 3,733,238 issued to Long et al. on May 15, 1973. Long et al. describe mechanism for producing laminated sheet materials and particularly for welding together layers of thermoplastic materials by the use of ultrasonic vibration equipment. A plurality of spaced ultrasonic vibration transmitting members having working surfaces in direct contact with one side of the sheet-like elements is employed in cooperation with opposing spaced anvil surfaces located on the opposite side of the sheet-like elements to produce full width webs of thermoplastic laminated material.
Commonly assigned U.S. Pat. No. 4,404,052 issued to Persson et al. on Sept. 13, 1983 also discloses prior art method and apparatus for continuously ultrasonically bonding together a plurality of juxtaposed webs to form a laminate structure as the webs are being driven forward at a relatively high velocity. Persson et al. teach that the regions of the webs to be bonded are subjected to progressively increasing compressive forces while simultaneously being subjected to ultrasonic energy as they traverse a portion of a predetermined path at a predetermined velocity.
Commonly assigned U.S. Pat. No. 4,430,148 issued to Schaefer on Feb. 7, 1984 discloses still another prior art continuous ultrasonic bonding system wherein a discrete pattern of protuberances is so configured and disposed on the anvil in its machine direction as to obviate cobblestoning of the transducer with respect to the anvil as a patterned portion thereof is moved past the transducer tip. The discrete pattern of protuberances is preferably so configured and disposed transverse the apparatus to precipitate wear--preferably even wear--of the tip of the ultrasonic transducer of the apparatus along the entirety of a line-of-contact portion thereof.
Other exemplary ultrasonic bonding systems of the prior art are disclosed in U.S. Pat. No. 3,879,256--Russ; U.S. Pat. No. 3,993,532--McDonald et al; U.S. Pat. No. 4,146,416--Goldman; U.S. Pat. No. 4,311,540--Hill; and U.S. Pat. No. 3,562,041--Robertson. The latter reference discloses an ultrasonic laminating apparatus wherein the bonding pattern comprises a continuous line which closes upon itself.
While the prior art discloses method and apparatus which have been developed to overcome many of the problems of continuously bonding webs to one another on-the-fly without use of an ancillary adhesive, it is believed that the majority of these methods have been limited to situations wherein each of the webs to be bonded is capable of being locally melted or at least softened sufficiently to permit localized bonding.
Furthermore, the known prior art has not solved all of the problems associated with continuous on-the-fly adhesive-free web bonding or laminating operations. This is particularly true with respect to web bonding operations using one or more substantially stationary elements to input mechanical energy to the webs to effect bonding. In the case of ultrasonic bonding processes using a substantially stationary vibrating ultrasonic horn, web damage due to tearing, web damage due to web jamming, and web damage caused by sticking of the web or webs to the elements used to input mechanical energy are frequently experienced. These problems are generally more acute when one or more of the webs to be bonded is relatively weak, when one or more of the webs is highly compressible and/or when the incoming web speeds are very high. Furthermore, the known prior art systems do not exhibit an ability to concentrate and retain the heat generated in the web or webs to be bonded rather than being lost to the elements used to input the mechanical energy.
Accordingly, it is an object of the present invention to provide method and apparatus which will permit continuous, high speed, adhesive-free mechanical web bonding on-the-fly, i.e., while the webs are being forwarded in juxtaposed relation, without significant web damage.
It is another object of the present invention to provide continuous method and apparatus for bonding on-the-fly one or more webs which can be locally melted or softened by inputting a given amount of mechanical energy thereto to one or more webs which exhibit a significant interstitial void volume, but which need not be locally melted or softened by the input of the same amount of mechanical energy, all without damaging any of said webs.
It is another object of the present invention to provide continuous method and apparatus for bonding on-the-fly one or more locally meltable or softenable polymeric webs to one or more resilient, highly compressible webs without damaging any of said webs.
It is another object of the present invention to provide continuous web bonding method and apparatus wherein most of the heat inputted to or generated in the webs being bonded is concentrated and retained in the webs rather than being lost via conduction to the mechanical elements utilized to input energy to the webs.
It is another object of the present invention to provide a laminate structure which is bonded on-the-fly without the use of an ancillary adhesive, said laminate structure comprising a pair of locally meltable polymeric webs located adjacent the outermost surfaces of a resilient, highly compressible web exhibiting a significant void volume, said polymeric webs being bonded to said compressible web by mechanical entanglement with the compressible web as well as to one another through the interstices comprising the void volume in said compressible web.
It is still another object of the present invention to provide the aforementioned benefits in a simple yet effective manner which does not significantly increase the cost of the resultant laminate product.